Electrical wires enter and exit a number of electrical boxes, control panels and walls as they carry electrical energy from source to load. The larger the load, the higher the rating of the equipment and the larger the wire must be to supply it. For 100-amp panels, which are generally the smallest in use, a #1 American Wire Gauge ("AWG") wire size could be used. For a 225-amp panel, #4/0 AWG would be required. While for a 600 amp panel 1000 kcmil wire would be required.
The physical route the wires follow necessitates bends in the wire at many locations. For example, an electrical circuit made up of a number of wires may run above a ceiling or through a wall until it reaches an electrical box containing circuit breakers, relays, controls or other devices. For electrical circuits passing through a wall or floor, the wires must often change direction before continuing along their route. To enter an electrical box the wires must change direction before reaching their connection point. In a three phase circuit having three or four wires, each wire has a different connection point.
Electrical wires are generally a single or multiple strand metallic conductor covered with a non-conducting material. Good engineering practice as well as governmental regulations limit how sharply a wire may be bent to prevent damage during operation. This limit is known as the minimum bending radius and is a multiple of the diameter of the wire. It should be noted that it is also physically difficult for a worker installing a wire having a larger conductor with a still insulation to make sharp bends.
The nominal diameter of a 1/0 AWG wire with insulation rated for 600 volts is slightly less than 1/2 inch. Its minimum bending radius is between approximately 21/2 and 31/2 inches. 1000 kcmil wire with insulation rated for 600 volts is slightly less than 11/4 inches and its minimum bending radius is between approximately 61/2 and 91/4 inches.
When a wire enters an electrical box at the bottom and must then enter a connection point some distance laterally and upward in the box, the wire must make a first lateral bend and then at least one second bend upward into the connection point. Using the 1/0 AWG wire described above, the lateral bend will require at least 2.5 inches before the point where it must bend upward, and then requires at least another 2.5 inches for the upward bend. If, however, the wire can enter the box directly outside the connection point, it is not necessary to allow for the lateral distance required for the second bend. In the example, at least 2.5 inches less space is needed.
Short circuits, often called "faults" are known to occur in electrical systems. Typical small commercial businesses have to withstand 50,000 to 100,000 amperes, while a shopping center or small industrial facility would be twice as high. A sudden inrush of fault current can produce electromagnetic forces of sufficient magnitude to move the wires substantially if they are not properly restrained. Good engineering design practice takes into account how much wire movement would occur if a zero resistance short circuit, known as a "bolted fault" were to occur between one or more energized wires and ground or between two or more energized wires. Wires entering an electrical box or passing through a wall or floor must be restrained sufficiently to withstand the movement which would otherwise occur during a bolted fault.
Electrical panel boxes are generally manufactured of a metal, with a plurality of partially cut through openings or removable plugs, known as "knockouts". The knockouts have an approximately circular shape and are located around the sides and back of the boxes. Knockouts have historically had a generally circular shape due to tooling limitations for making other shapes. An appropriate knockout is removed to create an opening through which each electrical wire may pass for electrical connection to the enclosed electrical device. Once a knockout has been removed it cannot be reinstalled.
A knockout of approximately the size of an entering wire provides some restraint in the event of a fault. However, an additional concern arises when the phase wires enter an electrical panel box through separate knockouts. The electromagnetic fields which tend to cancel each other when the wires of multi-phase circuits are in proximity, do not do so when the individual phase wires are separated. Magnetic fields and eddy currents can be generated in the metal panel box wall. Their magnitude varies with the amount of current being carried in the wires.
Standard knockout locations frequently are not directly in line with the desired connection point of the electrical device enclosed within the box. Therefore one or more bends in the wire inside the electrical box must be made to route the wire from the knockout location to the connection point. In order to accommodate a variety of knockout locations as well as a variety of bending radii, electrical boxes are larger than would be required if wires could enter the box in a straight line into the connection point.
Thus there exists a need for a system and method for installation of electrical wiring into electrical boxes and through openings in control panels and walls, eliminating additional space requirements to accommodate wire bends due to nonaligned connection points and electrical box entry points. Smaller boxes increase the design options for architects and engineers for new installations as well as in electrical upgrades and retrofits for existing installations.